High-efficient inverting buck-boost converter with fully digital-controlled switch width modulation for microdisplays

Abstract

This letter proposes a highly efficient inverting buck-boost converter at light-load for microdisplay applications. The proposed buck-boost converter, which operates in discontinuous conduction mode, achieves high efficiency by modulating the switch width according to the sensed on-duty of the main power switch using the full-digital method. It generates an output voltage of -4 V using an input voltage of 1.8 V for a maximum load current (I-LOAD) of 20 mA. The proposed converter was fabricated in a 0.18 m bipolar CMOS DMOS (BCDMOS) process and measured to verify its performance. The measurement results showed that the proposed buck-boost converter achieved a maximum efficiency of 89.3% at I-LOAD of 20 mA and a high efficiency of up to 81.9% at light-load, where I-LOAD is <5 mA.